The present invention relates to the CRT""s stem portion and an improved shape of the stem that allows more uniform and airtight sealing between the neck and the stem.
Referring to FIGS. 8 and 9, a CRT has a face panel 15, a funnel portion 25, and a neck portion 3. The CRT displays images when electron beams 13 emitted from an electron gun 11 installed in the neck portion collide with phosphors 17 coated on the inner surface of the face panel 15. The electron gun 11 is secured on a flat disk-like stem 1, made of glass. A plurality of pins 23 penetrates the stem so that one end of each pin is connected to an electrode 21 of the electron gun 11 while the other end is connected to an external signal source for providing control current to the electrodes 21. The electrodes 21 focus and accelerate electrons emitted from a cathode 19 into beams. Once the electron gun 11 is supported by the pins 23 of the stem it is inserted into the neck portion 3 of a CRT. FIG. 10 shows a conventional method of sealing the stem to the end of the neck. The stem 1 is inserted somewhat into the neck 3 and the outer neck area corresponding to the stem base 5 is heated by a torch flame 7 until they are fused and sealed together. The remaining portion of the neck below the stem is cut away. However, in the process minute glass particles might find their way into the neck through the evacuation tube 9, adversely affecting the performance of the CRT. As a solution to this drawback another conventional method, as shown in FIG. 11, was devised where the diameter of a stem base 5 is about the same as the outer diameter of the neck end. Therefore, instead of being inserted into the neck the periphery of the upper surface of the stem contacts the cross section 3a of the neck end before fused together. But this alternative has its own drawback. Since the neck is made by cutting a long glass tube its cross section is not necessarily completely flat and smooth. A result is that it is placed on the flat surface of the stem there happens to be slight undesirable space indicated by t in FIG. 12 between the neck cross section 3a and the stem surface. This space causes tiny holes in the sealing surfaces. The torch flame may enter the neck through the holes possibly damaging parts of the electron gun by oxidizing the cathode support and stem pins.
An objective of the present invention is to provide a uniform sealing between the neck and the stem. Space between the surfaces of the neck end and the stem to be contacted together are minimized by raising either central or peripheral portion of a stem so that the neck end. The neck is more securely supported on the stem prior to fusion and this helps non-porous sealing of the neck end.